The Fibroblast Growth Factor (FGF) and Fibroblast Growth Factor Receptor (FGFR) proteins are involved in a number of cell signalling events. There are 4 different FGFRs (FGFR1, FGFR2, FGFR3, and FGFR4), each with different specificities for the 22 different FGFs. In addition, some of the FGFRs are alternatively spliced, giving rise to further patterns of ligand specificity. For example, FGFR2 IIIb is generally expressed in epithelial tissue and is activated upon binding by one set of FGFs whereas FGFR2 IIIc is generally expressed in mesenchymal tissue and is activated by a different set of FGFs.
Certain cancers and genetic disorders are characterized by activating mutations in the FGFR2 amino acid sequence. For example, subsets of patients with various cancers, such as endometrial, breast, lung, gastric, and ovarian cancers, show mutations in FGFR2. (See, for example, the Catalog of Somatic Mutations in Cancer (COSMIC) at http://www.sanger.ac.uk/genetics/CGP/cosmic/ providing a repository of somatic changes reported in the FGFR family.) These FGFR2 activating mutations may occur in the extracellular domain, for example, at the hinge region between the IgII and IgIII domains or within the IgIII domain, or in the intracellular tyrosine kinase domain. (See FIG. 1.) In general, mutations in the IgII-IgIII hinge region and IgIII domain may alter the ligand specificity of the receptor, for example, increasing the affinity of the receptor for its normal ligands and/or increasing the promiscuity of the receptor for various other ligands. Thus, these mutations are ligand dependent, meaning that their effects depend on the binding of FGFR2 to one or more of its ligands. In some instances, an alteration in the RNA splicing pattern of the mutant FGFR2 may be observed. In contrast, mutations in the tyrosine kinase domain are thought to be generally ligand independent, meaning that the FGFR2 is active in both the presence and the absence of its ligands.
Endometrial cancer, for example, is a common cancer in industrialized countries but has poor survival rates for those who cannot be treated surgically. Currently the majority of patients are treated with hysterectomy, while there are no curative treatments for patients whose cancers either cannot be surgically resected or whose cancers recur after surgery. Hence, there is a need for non-surgical treatments for this cancer. Several publications have reported that FGFR2 mutations are present in about 15-16% of endometrial carcinomas. (See, e.g., P. M. Pollock et al., Oncogene 26: 7158-7162 (2007); A. Dutt et al., Proc. Nat'l. Acad. Sci. USA 105(25): 8713-8717 (2008); M. Katoh, Int. J. Oncol. 33: 233-237 (2008); WO2008/118877; WO2005/115363.) Several such mutations are located in the IgII-IgIII hinge region and IgIII domain of FGFR2. A commonly observed FGFR2 mutation in endometrial tumor cells is S252W, found in about 7% of cases. In addition, a P253R mutation was found in about 2% of endometrial cancer cases. (See Id.; FIG. 1.)
These S252W and P253R mutations are the same mutations found in the germline of patients with the genetic disease Apert Syndrome, which causes craniosynostosis and syndactyl). Structural and biochemical studies of the FGFR2 S252W mutant receptor suggest that S252W and P253R mutants may cause the FGFR2 protein to bind more tightly to its normal FGF ligands as well as to bind other FGF ligands to which it normally does not bind. (See K. Yu et al., Proc. Natl. Acad. Sci. USA 97: 14536-41 (2000); O. A. Ibrahimi et al., Proc. Natl. Acad. Sci. USA 98: 7182-87 (2001).) In addition, FGFR2 is alternatively spliced and its function is regulated in part through the expression of different splice isoforms with different ligand specificities in different tissues. For example, Yu et al. (Proc. Natl. Acad. Sci. USA 97: 14536-41 (2000)) reported that the FGFR2 IIIb form is expressed in epithelial cells and may be activated upon binding to FGF7 and FGF10 whereas the FGFR2 IIIc form is expressed in mesenchymal cells and may be activated by binding to FGF2, FGF4, FGF6, FGF8, and FGF9. (See also FIG. 1.) Yu et al. also reported that the S252W mutation may disrupt this splicing-based regulation of FGFR2 function. The S252W FGFR2 IIIb form not only may bind more tightly to its normal ligands such as FGF7 and FGF10, but it may also be activated by the FGFR2 IIIc ligands FGF2, FGF6, and FGF9.
The present invention relates to the use of R1Mut4 to treat cancers, for example endometrial cancers, characterized by expression of an FGFR2 IIIb protein with a point mutation at position 252 and/or position 253, such as S252W or P253R. The present invention also relates to the use of other FGFR1 ECDs to treat cancers characterized by ligand-dependent activating mutations of FGFR2, such as, for example, endometrial cancer.
The present inventors have found that an FGFR1 ECD fusion molecule called R1Mut4 (SEQ ID NO:22) inhibits the growth of endometrial carcinoma cells expressing an S252W mutant FGFR2 IIIb protein, both in vitro and in a mouse xenograft model. (See FIGS. 2-7.) In the mouse xenograft model, R1Mut4 dramatically inhibited growth of a tumor derived from endometrial carcinoma cells carrying the FGFR2 S252W mutation. (See FIG. 7.) The present inventors have also found that R1Mut4 inhibits tumor growth in a dose-dependent fashion in a therapeutic (or established) xenograft endometrial cancer model using human endometrial carcinoma MFE-280 cells with a S252W mutated FGFR2 genomic locus. (See FIG. 8.) Furthermore, R1Mut4 partially inhibited cell growth in the HCC1143 breast carcinoma cell line carrying the FGFR2 R203c mutation. (See FIGS. 9 and 10.)
The present invention also relates to inhibiting the growth of tumor cells expressing either the point mutation serine 252 to tryptophan of the FGFR2 protein or the point mutation proline 253 to arginine of the FGFR2 protein, comprising exposing the tumor cells to an amount of an FGFR1 ECD fusion molecule comprising the amino acid sequence of SEQ ID NO:22 effective to inhibit growth of the tumor cells.
The present invention further relates to treating a cancer in a subject, comprising administering a therapeutically effective amount of an FGFR1 ECD fusion molecule comprising the amino acid sequence of SEQ ID NO:22 to the subject, wherein the cancer is characterized by having tumor cells expressing either the point mutation serine 252 to tryptophan of the FGFR2 protein or the point mutation proline 253 to arginine of the FGFR2 protein.